The present invention relates to a printer, and more particularly to a paper feeder capable of feeding many types of recording paper and of reliably feeding all of the many types of recording paper.
Various types of recording paper are used on printers such as wire dot-matrix printers.
FIG. 3 of the accompanying drawings illustrates a continuous paper Sa known as a fan-fold stack. The continuous paper Sa has feed holes P called perforations defined in each edge thereof at prescribed intervals. FIG. 4 shows a roll of paper Sb which does not have the feed holes P.
FIG. 5 shows a conventional printer which uses the unperforated roll of paper Sb. In this printer, the roll paper Sb is inserted from behind a base 1 and rolled around a cylindrical platen 2 from below the same. The paper Sb is held against the platen 2 by means of rollers 5 mounted on a paper holder shaft 4. The platen 2 has a shaft 3 rotated by any suitable drive mechanism such as a stepping motor (not shown) for vertically feeding the paper Sb sandwiched between the platen 2 and the rollers 5 in response to rotation of the platen 2. A carriage 7 is slidably mounted on a carriage guide shaft 6 extending parallel to the platen 2, and supports thereon a printing member 8 such as a wire dot-matrix head or a thermal head. The printing member 8 is disposed in confronting relation to the roll paper Sb rolled around the platen 2. Power from the stepping motor (not shown) is transmitted to the carriage 7 through a wire or the like to move the carriage 7 and the printing member 8 on the guide shaft 6 in a direction along the platen 2 for effecting desired printing operation.
The printer shown in FIG. 5 is disadvantageous however because the paper feed operation lacks reliability when the paper Sb is fed along under the pressure which it is subject to, sandwiched between the platen 2 and the pinch rollers 5. More specifically, paper feed pitches may be subjected to slight variations due to any error in the diameter of the platen 2 and slippage between the paper Sb and the platen 2. Where the paper Sb is ruled and characters are to be printed along the ruled lines, the line feed pitches tend to be out of alignment with the intervals of the ruled lines as the platen 2 rotates.
The continuous perforated paper Sa shown in FIG. 3 is more suitable for printing on the ruled lines. In case the continuous paper Sa is used, it is necessary to employ a special dedicated arrangement in which paper feed pins are mounted on the platen 2 or an arrangement shown in FIG. 6 in which a tractor feed mechanism is added to the arrangement of FIG. 5.
The tractor feed mechanism denoted by numeral 10 in FIG. 6, is attached upwardly and slightly rearwardly of the platen 2. The tractor feed mechanism 10 has side frames 11a, 11b and a pair of shafts 12, 13 extending parallel to each other between the side frames 11a, 11b. One of the shafts 13 is rotatably driven by a stepping motor (not shown). Blocks 14a, 14b are mounted respectively on opposite ends of the shafts 12, 13 and spaced a given distance from each other, with a belt 15 wound around each of the blocks 14a, 14b. The belt 15 is formed of a resilient material such as rubber or silicone and has a plurality of pins 15a disposed on a peripheral surface thereof at regular pitches equal to those of the feed holes P in the continuous paper Sa. Rotation of the shaft 13 driven by the stepping motor is transmitted to the belt 15 to rotate the same at a prescribed speed around each of the blocks 14a, 14b.
The continous paper Sa is fed from behind the base 1 into a position below the platen 2 and then rolled around the platen 2. The feed holes P in the continuous paper Sa are fitted over the pins 15a on the belts 15. Paper holder plates 16 (one shown) are mounted respectively on the blocks 14a, 14b for preventing the continous paper Sa from being detached from the blocks 14a, 14b. The paper holder shaft 4 is pulled toward the front of the base 1 for separating the rollers 5 off the platen 2. During printing operation, the carriage 7 is moved laterally and the printing member 8 is operated to record desired characters on the continuous paper Sa. For line feeding operation, the shaft 13 is driven by the stepping motor to rotate the belts 15. The continuous paper Sa is now fed along accurately by the pins 15a on the belts 15.
The conventional printer shown in FIG. 5 allows only the roll paper Sb or separate sheets to be used thereon, but does not permit the continuous perforated paper Sa as shown in FIG. 3 to be employed. If it is desired to use the continuous paper Sa on the printer of FIG. 5, then it is necessary to add the tractor feed mechanism 10 as illustrated in FIG. 6. The resultant construction of the combined device is complex. Furthermore, it involves an expenditure of time and labor to attach and detach the tractor feed mechanism 10. On the other hand, a printer originally equipped with the tractor feed mechanism 10 cannot use the roll paper Sb or plain separate sheets thereon.